Semiconductor chip fabrication is a complicated process that involves a coordinated series of precise operations. It is well known that during the various steps in these operations, the surfaces of the semiconductor substrate (i.e., semiconductor wafers) become contaminated with a layer of residue comprised of particulates, organic materials, metallic impurities (e.g. copper, aluminum, titanium, tungsten, etc.), and native oxides (e.g., silicon dioxide).
An example of wafer contamination created as a result of a manufacturing operation can be seen in FIG. 1A, which shows a plasma etching process being employed on a semiconductor wafer 100. Semiconductor wafer 100 is in a plasma etching chamber. The surface of semiconductor wafer 100 is coated with a photoresist material 104 which protects areas of the wafer surface from etching. Etching is a well known method to remove material from the surface of a wafer to create microscopic patterns which conform to an integrated circuit (IC) design. Plasma 110 is directed at the surface of semiconductor wafer 100 to initiate etching on the wafer. Areas of the wafer surface not protected by the photoresist material 104 are etched by plasma 110 to form trench structures in the oxide layer of the semiconductor substrate. The area not protected by photoresist 104 shows that a plume of etched material 102 can form as the result of plasma etching. The plume showers etched material onto the wafer surface and on the sides of the etched trenches. This material can then interact with other contaminants on the wafer to form a contamination film (known as post etch residue).
After plasma etching, photoresist 104 is typically removed through a process called ashing to strip the photoresist material from the wafer surface. FIG. 1B shows the contamination on the wafer surface that can result after plasma etching and ashing operations have completed. As shown in FIG. 1B, the wafer has a variety of contamination species 120 which can include post etch residue, residual photoresist material, sputtered metals, and metal oxides.
Removal of these contaminants is a vital step in producing ICs because contaminants on a wafer surface cause defects in the IC which result in decreased reliability or even failure of the IC. Therefore, the removal of contaminants from the wafer surface is necessary to produce the highest yield of viable devices per wafer.
Proprietary chemical formulations are available to remove post etch residues. However, these formulations are expensive to purchase in sufficient quantities for large scale wafer manufacturing. Furthermore, these proprietary chemicals often take several minutes to effectively remove the contaminants on the wafer surface. This delay can result in lower wafer output which adds to the expense of employing these formulations in the context of large-scale wafer manufacturing. Non-proprietary cleaning chemicals have been utilized in the past for wafer cleaning. However, the amount of contamination that remains on the wafer surface remains unacceptably high unless long process times are provided to clean the wafer surface. This is equally counterproductive to the goal of achieving high throughput wafer manufacture. Therefore in view of the foregoing, there is a need for methods to remove post etch residue chemicals that can effectively clean the surface of a wafer in a timely fashion.